Refining of pyrethrum oleoresins



Patented Dec. 24, 1946 REFININ G OF PYRETHRUM OLEORESINS Wayne E. Kuhn, Scarsdale, N. Y., assignor to The Texas Company, New York, N. Y-v a corporation of Delaware No Drawing. Application December 31, 1943, Serial No. 516,591

3 Claims. (Cl. 260-468) This invention relates to the refining of pyrethrum oleoresins to remove inactive and inert material.

Pyrethrum oleoresins are obtained from pyrethrum flowers by extraction of the flowers with organic solvents such as kerosene, alcohol, acetone, ethylene dichloride, etc. The resulting extracts contain the active principles including some inert materials. The active principles are understood to be pyrethrin-l and pyrethrin-Z which are viscous liquids, pyrethrin-l boiling at about 150 C. in absolute vacuum while pyrethrin- 2 decomposes when distilled in absolute vacuum.

These pyrethrins are commonly used in the manufacture of insecticides and particularly in the manufacture of insecticides which are used in liquid form suitable for use in various types of mechanical spraying devices.

The active ingredients dissolved in a solvent may be placed in cans or other metal containers for subsequent use. The solvent may be a liquefied normally gaseous material, and the resultin solutions are put up in small containers capable of withstanding high pressures, each container provided with a nozzle or spray through which the solution can be discharged in mist form into the surrounding atmosphere.

It has been found that upon standing for substantial periods of time, such as occur during transportation or upon storage in warehouses, separation of solid material of waxy and resinous character frequently occurs in the containers. This material apparently consists for the most part of relatively inert or inactive material. It is of a gummy nature and tends to cause plugging in the nozzles.

Accordingly the present invention has to do with effecting removal of this waxy and resinous inactive material by treatment with a solvent. A solvent which has been found eiTective for this purpose is a liquefied normally gaseous hydrocarbon such as propane. In accordance with the invention pyrethrum oleoresins and pyrethrum concentrates are subjected to treatment with a liquefied normally gaseous hydrocarbon such as propane at relatively low temperatures such that the undesired inert material is precipitated, while retaining the pyrethrins in solution, and the resulting precipitate removed.

More specifically, the pyrethrum oleoresins or pyrethrum concentrates are treated with liquefied propane in the proportion of about 2 to volumes of propane per volume of oleoresin at a temperature ranging from about +30 to 30 F. There is thus formed a solution of oleoresins containing the active principles dissolved in the bulk of liquid propane leaving a precipitate of insoluble material of waxy and resinous character and of greenish brown color.

The precipitate is removed and thereafter the propane may be removed from the extracted oleoresins. Removal of the propane is readily accomplished due to its volatile nature and the relatively high boiling temperatures of the oleoresins.

The precipitate removed from the oleoresins is soluble, at least to a large extent, in solvents such as acetone, petroleum ether, and pentane at these low temperatures.

The extracted oleoresins from which the waxy and resinous material has been removed thus provide an improved product for the manufacture of insecticidal spray solutions. Solutions prepared from the refined oleoresins of my invention may be kept in containers and spray vessels for long periods of time Without formin objectionable precipitates of solid and semi-solid material.

By way of specific example, pyrethrum oleoresins containing about 31% pyrethrins were dissolved in liquefied propane in the proportion of about 5 volumes of propane to 1 volume of resins. The resins were completely dissolved in the propane at about F. and the resulting solution was chilled to about 30 F. and subjected to settling, forming soluble and insoluble phases. The soluble phase was drawn off.

The remaining insoluble phase was washed at 30 F. with 1.5 volumes (basis original charge) of propane chilled to -30 F., and again settled. The resulting wash solution was drawn oil and the remaining insoluble phase was then given another and final wash with the same quantity of additional propane at the same temperature and in the same manner.

The two wash solutions were mixed with the first mentioned soluble phase and the solvent removed from the mixture. The resulting solvent free-pyrethrin concentrate amounted to about 39.9% of the original oleoresin charge by weight, this concentrate consisting of about 78% pyrethrins.

The insoluble resinous material remaining from the final washing operation amounted to about 60.1% by weight.

When extracting another sample of the oleoresin charge with normal pentane under the same conditions of temperature and solvent dosage and following the same procedure, the soluble phase amounted to about 78.3% as compared with only 39.9% in the case of propane, so that the pentane is much less selective than propane.

While the foregoing extraction was carried out as a multiple batch treatment nevertheless it is contemplated that the treatment may be carried out in a continuous manner employing a countercurrent system. Thus the treatment may be effected in a tower packed with inert packing.

1. The method of refining pyrethrum oleor es- I ins to obtain a pyrethrin concentrate substantially stable against resin separation during storage which comprises dissolving said pyrethrum oleoresins in from about2 to 10 volumes of liquid propane, chilling the solution to about -30 F. such that a soluble phase and an insoluble phase are formed, said soluble phase comprising pyrethrins dissolved in propane and said insoluble phase comprising constituents soluble in normal pentane at said temperature, removing said insoluble phase and removing propane from said soluble phase thereby forming a solvent-free concentrate consisting predominantly of pyrethrins.

2. The method of refining pyrethrum oleoresins to obtain a pyrethrin concentrate substantially stable against resin separation during storage which comprises extracting pyrethrin oleoresins containing about 31% pyrethrins with liq uid propane in the proportion of about 2 to 10 volumes of propane per volume of oleoresin feed, efiecting the extraction at a temperature of about 30 F. such that a soluble phase and an insoluble phase are formed, said soluble phase comprising pyrethrins dissolved in propane and said insoluble phase comprising constituents soluble in normal pentane at said temperature, separating said phases, and removing propane from said soluble phase thereby forming a solvent free concentrate consisting of about 78% pyrethrins.

3. The method of refining pyrethrum oleoresins ,to obtain a pyrethrin concentrate substantially stable against resin separation during storage which comprises extracting pyrethrum oleoresins containing a substantial amount of pyrethrins with liquid propane in the proportion of about 2 to 10 volumes of propane per volume of oleoresin feed,fefiecting the extraction at a temperature of about -30 F. such that a soluble phase and an insoluble phase are formed, said soluble phase comprising pyrethrins dissolved in propane and said insoluble phase comprising constituents soluble in normal pentane at said temperature, separating said phases, and removing propane from said soluble phase thereby forming a solvent free concentrate consisting predominantly of pyrethrins.

3 WAYNE E. KUHN. 

